The making of steel by the BOF furnace has increased considerably in recent years because of the high efficiency of this method, and therefore the lower cost of manufacture. In the BOF method, iron scrap, pig iron and lime are charged into the furnace, and an oxygen flame jets down on the charge. Lime is a major constitutent of steel making slags, but has an extremely high melting point (4568.degree. F) and it is impractical to raise the furnace temperature to the melting point of lime. To reduce the temperature necessary to fuse the lime, other agents were added to the furnace charge. One agent used almost exclusively in the BOF furnnace is fluorspar, and it has performed very well in its combination with lime.
However, good grade fluorspar has in recent years been in dwindling supply and therefore expensive. The main source of fluorspar is located in Mexico and importation not only represents transportation expense but also adversely affects the national balance of trade payments. The readily available supply of fluorspar is of poor quality and as a consequence steelmakers have been conducting extensive research to find a suitable fluorspar substitute. The search for inexpensive slag fluidizers still continues with the steelmakers.
In the melting of scrap aluminum, in which I am engaged, to produced relatively pure aluminum for use in steel making, the slag at the top of the molten aluminum is skimmed and thrown on a waste pile. Periodically this waste has to be hauled away to a dumping area, and this not only represented hauling expense but also affected the ecology because dumping areas are unsightly. Therefore, utilization of this waste produce not only creates a good source of a fluorspar substitute, but also provides such substitute at tremendous savings.
My invention proposes use of this waste product for combination with the lime in the furnace to lower the fluidizing temperature of the lime, and this waste product, being largely alumina, will perform in an acceptable manner.